net/9p abuses iov_iter primitives - attempts to copy _from_ a destination-only iov_iter when it handles Rerror arriving in reply to zero-copy request. Not hard to fix, fortunately; it's a prereq for the iov_iter_get_pages() work in the second part of iov_iter series, ended up in a separate branch. Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>